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                            <div style="color:gray; word-break: break-all; font-size:12px;">原文地址: <a href="https://www.elastic.co/guide/cn/elasticsearch/guide/current/sorting-by-distance.html" rel="nofollow">https://www.elastic.co/guide/cn/elasticsearch/guide/current/sorting-by-distance.html</a>, 版权归 www.elastic.co 所有<br/>
                            英文版地址: <a href="https://www.elastic.co/guide/en/elasticsearch/guide/current/sorting-by-distance.html" rel="nofollow">https://www.elastic.co/guide/en/elasticsearch/guide/current/sorting-by-distance.html</a>
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<b>请注意:</b><br>本书基于 Elasticsearch 2.x 版本，有些内容可能已经过时。
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<span class="breadcrumb-node">按距离排序</span>
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<h2 class="title">
<a id="sorting-by-distance"></a>按距离排序<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/310_Geopoints/50_Sorting_by_distance.asciidoc">edit</a>
</h2>
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<p>检索结果可以按与指定点的距离排序：</p>
<div class="tip admon">
<div class="icon"></div>
<div class="admon_content">
<p>当你 <em>可以</em> 按距离排序时， <a class="xref" href="sorting-by-distance.html#scoring-by-distance" title="按距离打分">按距离打分</a> 通常是一个更好的解决方案。</p>
</div>
</div>
<div class="pre_wrapper lang-json">
<pre class="programlisting prettyprint lang-json">GET /attractions/restaurant/_search
{
  "query": {
    "filtered": {
      "filter": {
        "geo_bounding_box": {
          "type":       "indexed",
          "location": {
            "top_left": {
              "lat":  40.8,
              "lon": -74.0
            },
            "bottom_right": {
              "lat":  40.4,
              "lon": -73.0
            }
          }
        }
      }
    }
  },
  "sort": [
    {
      "_geo_distance": {
        "location": { <a id="CO233-1"></a><i class="conum" data-value="1"></i>
          "lat":  40.715,
          "lon": -73.998
        },
        "order":         "asc",
        "unit":          "km", <a id="CO233-2"></a><i class="conum" data-value="2"></i>
        "distance_type": "plane" <a id="CO233-3"></a><i class="conum" data-value="3"></i>
      }
    }
  ]
}</pre>
</div>
<div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO233-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>计算每个文档中 <code class="word">location</code> 字段与指定的 <code class="literal">lat/lon</code> 点间的距离。</p>
</td>
</tr>
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO233-2"><i class="conum" data-value="2"></i></a></p>
</td>
<td align="left" valign="top">
<p>将距离以 <code class="word">km</code> 为单位写入到每个返回结果的 <code class="word">sort</code> 键中。</p>
</td>
</tr>
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO233-3"><i class="conum" data-value="3"></i></a></p>
</td>
<td align="left" valign="top">
<p>使用快速但精度略差的 <code class="literal">plane</code> 计算方式。</p>
</td>
</tr>
</table>
</div>
<p>你可能想问：为什么要制定距离的 <code class="word">单位</code> 呢？用于排序的话，我们并不关心比较距离的尺度是英里、公里还是光年。 原因是，这个用于排序的值会设置在每个返回结果的 <code class="word">sort</code> 元素中。</p>
<div class="pre_wrapper lang-json">
<pre class="programlisting prettyprint lang-json">...
  "hits": [
     {
        "_index": "attractions",
        "_type": "restaurant",
        "_id": "2",
        "_score": null,
        "_source": {
           "name": "New Malaysia",
           "location": {
              "lat": 40.715,
              "lon": -73.997
           }
        },
        "sort": [
           0.08425653647614346 <a id="CO234-1"></a><i class="conum" data-value="1"></i>
        ]
     },
...</pre>
</div>
<div class="calloutlist">
<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO234-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>餐厅到我们指定的位置距离是 0.084km。</p>
</td>
</tr>
</table>
</div>
<p>你可以通过设置 <code class="literal">单位</code>(<code class="literal">unit</code>) 来让返回的值符合应用程序的要求。</p>
<div class="tip admon">
<div class="icon"></div>
<div class="admon_content">
<p>地理距离排序可以对多个坐标点来使用，不管（这些坐标点）是在文档中还是排序参数中。使用 <code class="literal">sort_mode</code> 来指定是否需要使用位置集合的 <code class="literal">最小(min)</code> <code class="literal">最大(max)</code> 或者 <code class="literal">平均(avg)</code> 距离。
如此就可以返回 “离我的工作地和家最近的朋友” 这样的结果了。</p>
</div>
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<div class="section">
<div class="titlepage"><div><div>
<h3 class="title">
<a id="scoring-by-distance"></a>按距离打分<a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elasticsearch-cn/elasticsearch-definitive-guide/edit/cn/310_Geopoints/50_Sorting_by_distance.asciidoc">edit</a>
</h3>
</div></div></div>
<p>有可能距离是决定返回结果排序的唯一重要因素，不过更常见的情况是距离会和其它因素，比如全文检索匹配度、流行程度或者价格一起决定排序结果。</p>
<p>遇到这种场景你需要在 <a class="xref" href="function-score-query.html" title="function_score 查询">功能评分查询(function_score query)</a> 中指定方式让我们把这些因子处理后得到一个综合分。 <a class="xref" href="decay-functions.html" title="越近越好">越近越好</a> 中有个一个例子就是介绍地理距离影响排序得分的。</p>

<p>另外按距离排序还有个缺点就是<b>性能</b>：需要对每一个匹配到的文档都进行距离计算。而 <code class="literal">功能评分(function_score)</code>查询，在 <a class="xref" href="_Improving_Performance.html#rescore-api" title="结果集重新评分"><code class="literal">rescore</code> 语句</a> 中可以限制只对前 <em>n</em> 个结果进行计算。</p>
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